Mulching paper



Patented Aug. 3, 1954 MULCHING PAPER James W. Linehan, San Francisco,Calif., assignor to Crown Zellerbach Corporation, San Francisco, Califi,a corporation of Nevada No Drawing. Application July 25, 1950, SerialNo. 175,877

1 Claim. l

The present invention relates in general to agricultural mulching of thesoil, and, more specifically, to that type of mulching which consists inthe covering of the cultivated ground between individual plants withsheet material,

particularly, layer of heavy paper.

Within recent years it has been discovered that heavy paper, such askraft paper, when treated with on, can be empioyed in this manner as amulching medium with beneficial results. The

oiling of the paper not only prolongs the life of the itseh in thefield, but, when such oil as crude petroleum oil is used for treatingthe paper, it has been observed that the oil treated paper efficientlyprevents weed growth and also causes more ground heat and groundmoisture to be retained in the soil beneath the oiled paper. in myopinion this prevention of weed growth and retention of ground heatbeneath such mulching paper are partly due to the dark color of the oilas well as to the chemical of the composition of the crude oil, sincethe dark color undoubtedly acts to shut ed the light rays from thecovered ground, retarding the development of plant life beneath thepaper and thus cooperating with the effectiveness of the chemicalcomposition of the oil in stopping weed growth. The dark color alsopromotes the absorption and retention of heat beneath the paper. Thiswould account in part for the higher ground temperature which has beenfound to prevail when such oil treated mulching paper has been used.

Mulching paper treated with crude petroleum oil is now beginning to beused quite extensively, for example in pineapple growing. Variousexperiments convinced me that more efficient results are attainable if agreater amount of crude oil is used in the paper, and further that stillbetter results can be obtained if the oil treated paper is also madesubstantially black in color and particularly if the paper is renderedopaque. The kraft paper which is now being used for mulching is notcapable of holding the optimum amount of oil which I find desirable formulching paper. Attempts to increase the amount of oil in the mulchingpaper have shown that the mulching paper heretofore used is not capableof holding such optimum amount of oil. The heavy kraft paper which iscustomarily employed as mulching paper reaches a saturation point of oilwh n the amount of oil by weight is from 40% to 50% of dry fiber weight,whereas I have found that up to twice this amount of oil is desirable.Heretoforc if the amount of oil applied to the paper happened slightlyto exceed the saturation level, some drainage of oil from the paperwould then occur during the shipment or storage of the paper, thusresulting in an undesirable condition. One of the objects of my presentinvention is to provide an improved oil-impregnated mulching paper whichwill be capable of holding a larger amount of oil effectively, such ascrude petroleum oil.

Another object of my invention is to provide an improved oil-impregnatedmulching paper which will be more efiicient in absorbing and retainingheat and increasing ground temperature.

A related object is to provide an improved mulching paper which will notonly carry a large amount of oil, the chemical characteristics of whichact to retard weed development, but which mulching paper will alsoinhibit weed growth by effectively shutting off the rays of light fromthe ground.

Oil-treated mulching paper generally and preferably consists of heavykraft paper treated with crude oil, as previously mentioned, and a verysatisfactory oil which is being used for this purpose is the ends oilknown to the trade as Bunker 0 Fuel Oil. The oil treated kraft paper ismanufactured, sold, and shipped in rolls of convenient size; forexample, the rolls are customarily about one foot in diameter andapproximately three feet in length.

One .difiiculty I have observed in connection with such rolls ofoil-treated mulching paper is when the mulching paper is unrolled in thespreading of the paper on the ground, there is a strong tendency for thelayers of the oiled paper to stick together. Coating of the heavy oilex- "t-nding over the smooth surface of the paper in each layer of theroll produces a surface tension whicl'i makes the unrolling of the paperdifficult and frequently results in the breaking of the paper duringrapid unrolling or" the A further object of my invention is to producean improved oil-treated mulching paper with which this particulardifiiculty will be practically elimins-ted.

The breaking or tearing of the mulching paper after it has been laid inthe field, or even while it is being laid, is a further well knownsource of trouble and annoyance. There are several reasons why suchbreaks occur. If the paper is stretched over rough stones or hardsun-baked clcds, these may puncture the paper. The holding down of theedges of the paper with stones, as is frequently done, may also causetears or punctures. If the row to .be covered by the paper is curved, anextra strain is placed on one edge of the paper as it is unrolled andthis strain may cause breaks to start in that edge of the paper. If thepaper is stretched over the ground too tightly and weighted down alongthe edges with stones, the shrinkage or contraction of the paper as itis subjected to the alternate effects of hot sun and light rains or dewmay be sufficient to produce breaks in the paper. A one thousand footstrip of mulching paper will contract as much as ten to 20 feet duringnormal exposure and consequently ordinary mulching paper which has beenstretched near to the maximum point during the laying of the paper onthe ground will crack under the strain of such contraction or shrinkage.

It will be obvious that the breaking or tearing of the paper under anyof these conditions will necessitate an additional expenditure of timeand labor in covering of such breaks or tears, for if the resultingopenings are not taken care of the weed growth will then develop in suchplaces on a very rapid scale. An important object of my invention is toprovide an improved mulching paper which will have considerably greatercapacity for stretching and thereby reduce the probability of breaks andtears occurring under such conditions as those above indicated.

In carrying out my invention I prefer to use kraft paper of thecustomary weight and grade heretofore used for mulching paper, thus, forexample, paper which might be described as 100% natural kraft paperhaving a basis weight of 62 to 65 pounds (the basis weight forconvenience being figured as the weight of 500 sheets of paper 24" x 36in size). Other weights and grades of paper, however, can also be usedwith my invention.

A necessary and most important step in the carrying out of my inventionis that the paper used is creped, thus for example, machine creped witha creping doctor in the well known manner, so that the creped paper,after oiling, will have a stretch in the machine direction of from toThe paper, creped in this manner and to the extent indicated, is thenimpregnated with crude petroleum oil, for example the Bunker C Fuel oil.The impregnating of the creped paper with oil may be accomplished invarious ways but I have found it convenient and satisfactory to use thesame equipment as used in waxing paper. Although in the case of the samepaper when uncreped, the oil saturation point will be reached when theamount of oil by weight is equal to from 40% to 50% of dry fiber weightof the paper, the creping of the paper will enable approximately twicethe amount of oil to be satisfactorily carried by the paper. One reasonfor this is the fact that the creping of the paper makes its capacityfor absorption greater. The minute breaking of the sheet fiberstructure, as a result of the creping operation, increases the porosityof the sheet and also causes it to be a more adsorptive medium. Anotherreason why the creped paper will satisfactorily carry this desirableincreased amount of the crude oil is the fact that when the oiled crepedpaper is wound in the customary roll, the creped layers do not contacteach other over the entire surface area. Thus the surface tension of theoiled paper in the roll is considerably reduced. This produces a relatedadvantage of facilitating the unrolling of my improved mulching paper inthe field.

A specific example of my improved mulching paper, which has been foundto be very satis- 4 factory in extended tests, is a creped,oil-impregnated paper made from natural kraft paper having a basisweight (500 sheets 24" x 36") of 62 pounds. The creped paper isimpregnated with Bunker Fuel Oil, thus for example, fuel oil with aviscosity of 160-185 seconds Saybolt at F. and enough of the oil isadded to bring the basis weight up to 120 pounds. The stretch of thecreped paper in the machine direction after oiling approaches 7%. Thepaper is made up into rolls approximately 12 inches in diameter, thewidth of the paper being from 34 inches to 36 inches. No oil leakagefrom the paper in the rolls takes place at an time during the storage,shipping or handling of the rolls. The paper unrolls freely in the fieldand the paper on the ground conforms to unevenness of the ground andeven adapts itself to curved rows on the ground. Instances of breakingor tearing of this paper have been rare and are insignificant incomparison with the breaking and tearing which occurs under similarconditions with the uncreped mulching paper heretofore To the best of myknowledge, all attempts heretofore made to produce a mulching paperwhich would have less tendency to break or tear under the conditionspreviously mentioned, have been aimed at making the paper heavier and ofhigher specific tensile strength, on the theory that this was what wasneeded in the paper. By specific tensile strength is to be understoodthe strength of a unit width determined by a standard testing machine.However, I have found that heavier paper and paper of higher specifictensile strength showed high breakage in the field. In the carrying outof my invention I have taken the opposite course inasmuch as the crepingin my improved mulching paper tends to lower the specific tensilestrength, but I have found that specific tensile strength is ofsecondary importance when high stretch value is imparted to the paper.In fact, with my invention, I have found that paper of lighter weightand lower specific strength can be satisfactorily used provided thepaper is machine creped so as to give the paper a sufiiciently greaterstretch while also producing an irregular surface in the paper to causethe area of contact of the layers of the oiled paper in the roll to bereduced. Of equal importance also is the fact that the creping makespossible the higher oil absorption per unit weight of fiber.

While the crude oil itself gives a somewhat dark color to theimpregnated paper, I have found that further improved results areobtained if dyes are incorporated in the paper to give it asubstantially black color. Another advantage is obtained byincorporating an opacifying pigment, such as carbon black, in thefurnish for the paper since an opaque paper shuts off from the groundthe light rays necessary for weed growth, and a paper which is black incolor absorbs a greater amount of heat and thus is instrumental inincreasing the temperature of the soil.

The oil-treated creped mulching paper can, if desired, have its wetstrength increased by the incorporation of melamine resin in the papermachine furnish. The addition of resin to the furnish increases theability of the paper to withstand the outdoor exposure to which mulchingpaper is subjected. For this purpose melamine resin to the amount of2.5% of the dry weight of the fiber may be incorporated in the furnish,following the customary technique in producing wet strength in paper.

I claim: Number Name Date An improved mulching paper of the character1,595,637 Wheildon Aug. 10, 1926 described for inhibiting weed growth,said mulch- 1,844,051 Allen Feb. 9, 1932 ing paper consisting of a heavypaper, creped su 1,882,377 Whittelsey Oct. 11, 1932 stantiallythroughout its extent, and impregnated, 5 1,882,713 Angier Oct. 18, 1932after creping, with a crude petroleum oil inimical 2,029,390 RodgersFeb. 4, 1936 to plant growth, the amount of such oil retained 2,333,959Smith Nov. 9, 1943 in the finished p p being f m 60% t 0% y 2,345,543Wohnsiedler Mar. 28, 1944 weight of the dry weight of the paper, thecreping of the paper serving to provide the necessary in- 10 FOREIGNPATENTS crease in the saturation level so as to enable the NumberCountry Dat paper to retain such high amount of the weed-in- 696,268France 13, 1930 hibiting oil and thereby enable said mulching pa- 531,18 many 5, 1931 per more effectively to prevent weed growth.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,315,362 Cumfer Sept. 9, 1919 2 1,332,141 Ohashi Feb. 24,1920 1,534,371 Finley Apr. 21, 1925 Farmers Bul. 1307, U. S. Dept. Agr.(Dec. 1931) on Quack Grass, page 21.

Cross, Handbook of Petroleum, Asphalt and Natural Gas pub. 1928 as Bul.25, Kansas City 0 (M0.) Testing Lab., page 472.

Porter, Petroleum Dictionary (1930), Gulf Pub. 00., Houston, 'I'ex., pp,94 and 95.

